Nagios - monitors your entire IT infrastructure

Nagios monitors your entire IT infrastructure to ensure systems, applications, services, and business processes are functioning properly. It provides centralized view of entire monitored IT infrastructure. In the event of a failure, Nagios can alert technical staff of the problem, allowing them to begin remediation processes before outages affect business processes, end-users or customers.

Nagios could be extended via Plugins. It is possible to monitor any probes (temperature, alarms...), which is capable of sending data to specific plugin. It has web and mobile interface for viewing current network status, notifications, problem history, log files, etc.

http://nagiosplugins.org/ lists all available plugins.